Fiber telemetry in wells is rapidly becoming a standard in the oilfield. One of the techniques for installing fiber sensors in the well is to use coiled tubing. Coiled tubing systems are well known in the oil and gas industry. The term normally connotes a relatively small diameter continuous tubing string that can be transported to a well site on a drum or in a reel. Methods for inserting coiled tubing systems into existing wells are known in the art. As oil and gas exploration technology continues to improve the demand for better wellbore information grows and there has been more interest in using coiled tubing to deploy more instrumentation into the wellbore, particularly pressure and temperature sensors.
Typically a fiber sensor based coiled tubing assembly consists of a number of discrete pressure sensors and FIMTs (Fiber In Metal Tubing), some of which act as temperature sensors themselves using DTS techniques (Distributed Temperature Sensing), or as acoustic sensors using DAS techniques (Distributed Acoustic Sensing) or as conductors of photonic information from the pressure sensors to the surface. As fiber optic telemetry develops there is increased need to install multiple fiber optic sensors inside coiled tubing. Each sensor may require its own FIMT, so there needs to be a method and devices to enable multiple FIMTs to be installed simultaneously in lengths of coiled tubing that can be up to 10 km.
With three pressure sensors and two fibers for DTS, there can be a total of 5 FIMTs that need to be fed into the tubing and come to the surface. A method for pulling the transducers and FIMT assembly into the coiled tubing in an orderly way to prevent sticking or jamming is required, which does not exceed the pulling strain limits of the FIMTs and their connections.
U.S. Pat. No. 6,116,085 to Moffatt describes a manufacturing method for inserting bundles of instrumentation, including thermocouples and pressure sensor wiring, in a coiled tubing system to create a continuous tubing string housing a plurality of pressure sensor assemblies connected to ports along the string and a plurality of thermocouples operative to measure temperatures along the string.
While some of these prior art methods provide workable solutions to the problem of installing sensor assemblies into coiled tubing there is a need for improved production techniques that do not require extensive cutting and welding steps in order to produce the coiled tube sensor assemblies. This need is growing as longer horizontal runs of tubing requiring more strength are being used.